Dependence of Basipetal Polar Transport of Auxin upon Aerobic Metabolism

Malcolm B Wilkins; Mary Martin

doi:10.1104/pp.42.6.831

Abstract

The movement of IAA-¹⁴C through coleoptile segments of Avena and Zea has been investigated under aerobic and anaerobic conditions. The results are as follows: Zea. Using a 5-mm segment and a 2-hour transport period anaerobic conditions reduced the total uptake of ¹⁴C from an apical donor by 74% and the proportion of the total found in the receiving block by at least 45%. Anaerobic conditions reduced total uptake from a basal donor by 58% but no ¹⁴C reached the apical receiving block in either air or N₂. Uptake from apical and basal donor blocks in N₂ is closely similar.

The presence of ¹⁴C in the basal receiving blocks, and its absence in the apical receiving blocks, in N₂ suggests that even in anaerobic conditions movement of IAA is polarized basipetally, although the movement occurs at only a fraction of the rate found in air.

Anaerobic conditions induced a similar reduction in basipetal movement of IAA in upper and lower 5-mm segments taken from the apical 10 mm of a Zea coleoptile.

Using 10-mm Zea segments no ¹⁴C was recovered in the receiving blocks at the basal end of the segment after 2 and 4 hours in N₂ whereas large amounts were recovered in air.

Avena: Using 5-mm segments and a 2-hour transport period the total uptake of ¹⁴C from an apical donor is reduced by 83%. Movement of ¹⁴C into the basal donor is totally inhibited in N₂. Total uptake of ¹⁴C from a basal donor is reduced by 61% in nitrogen and no ¹⁴C reached the apical receiving blocks regardless of the atmospheric conditions.

A time course for the movement of ¹⁴C into the basal and apical receiving blocks through 5-mm segments showed that in air the amount in the basal receivers increased for 4 hours and then remained approximately uniform. In N₂ no significant ¹⁴C reached the receivers until 6 to 8 hours after the application of donors but even then the amounts were about 12 to 14% of that in aerobic receivers. Movement of ¹⁴C into apical receivers was similar in air and in nitrogen and even after 6 to 8 hours the amount of radioactivity barely reached significant levels.